1. Technical Field of the Invention
The present invention relates to a method of adhesive bonding optical fibers and optical fiber cord and more particularly, to a method of adhesive bonding optical fibers in which a change in the property of the optical fiber which is caused by a stress of cure shrinkage of an adhesive applied for bonding the optical fiber to a ferrule or the like can be avoided and an optical fiber cord of the same.
2. Description of the Prior Art
FIG. 6 is a cross sectional view showing a conventional optical fiber cord.
The optical fiber cord 600 has a ferrule 30 bonded by an adhesive 20 to the end of an optical fiber core 15.
The optical fiber core 15 comprises an optical fiber 1, a cushion layer 2 of silicon resin or acrylic resin provided over the outer side of the optical fiber 1, and a cladding 3 of nylon or polyester provided on the outer side of the cushion layer 2. Portions of the cushion layer 2 and the cladding 3 at the end of the optical fiber core 15 are removed to expose the optical fiber 1.
The adhesive 20 is an epoxy resin material.
The ferrule 30 comprises a holder 31 made of stainless steel and a capillary 32 made of zirconia.
The exposed portion of the optical fiber 1 at the end of the optical fiber 15 is directly bonded at its outer side by the adhesive 20 to the inner side of the capillary 32 of the ferrule 30.
FIG. 7 is a flowchart showing steps of fabricating the optical fiber cord 600.
At Step J1, the end of the optical fiber 1 is exposed by removing the portions of the cushion layer 2 and the cladding 3 of the optical fiber core 15.
At Step J2, the optical fiber core 15 is inserted into the hollow in the holder 31 of the ferrule 30. Then, the exposed portion of the optical fiber 1 is inserted into the hollow of the capillary 32 of the ferrule 30 and bonded at its outer side by the adhesive 20 to the inner side of the capillary 32. Accordingly, the end of the optical fiber core 15 is arranged integral with the ferrule 30 hence constituting the optical fiber cord 600.
At Step J3, the end surface of the optical fiber cord 600 is polished so that light can run into and out from the end of the optical fiber 1.
When the optical fiber cord 600 employs a single-mode optical fiber core as the optical fiber core 15, a portion of single-mode light introduced to the other end of the optical fiber cord 600 may be mode shifted thus producing an interference mode which results in decrease of the optical coupling efficiency.
It was found through the perpetual studies of the inventors of this invention that the mode shift was caused by a force of stress resulting from the thermal shrinkage of the adhesive 20 used for bonding the end of the optical fiber core 15 to the ferrule 30.